Furnace construction and operation



May 29, 1928. I 1,671,395 D. BAIRD FURNACE CONSTRUCTION AND OPERATION Filed March 12,1926

Elvwenboz QM 301ml. 35 Qua/140134 Patented May 29, 192 8.

1 UNITED STATES v 1,671,395 PATENT OFFICE.

DUDLEY BAIED, OF BERKELEY, CALIFORNIA, ASSIGNOR TO NICHOLS COPPER COM- PANY, OF NEW YORK, N. Y.,

A CORPORATION OF NEW YORK.

FURNACE CONSTRUCTION AND OPERATION.

Application filed March 12, 1926. Serial No. 94,163.

This invention relates to furnaces and particularly to multiple hearth roasting furnaces, an example of which is shown in U. S. Letters Patent No. 976,175 to John B. F.

5 'I-Ierreshofi, dated November 22, 1910.

In furnaces of this type, there is often a large amount of dust exhausted with the gases therefrom, especially when dry, finely divided materials are under treatment.

When the process and novel form .of construction comprising this invention are utilized, the blowing and exhaust of dust is 1 greatly reduced and at the same time, re-

gardless of the type of material to be treated,

means are provided whereby temperature.

conditions within the furnace may be readily controlled to give the furnace eflicient and economical operative characteristics.

Various specific objects, features and advantages will more clearly appear from the detailed description given below taken in connection with the accompanying drawing which forms a part of this specification.

In the drawing, the figure illustrates in central vertical sectiona furnace embodying the invention.

In the furnace, as shown, a plurality of vertically spaced or superposed circular hearths are designated by the numerals 1 to 6 inclusive. These hearths are surrounded and supported in the usual manner by a cylindrical masonry furnace wall 7. The furnace wall in turn may be supported in any suitable well-known manner. The usual rovertically up 'tially along the central axis thereof and is here designated by the numeral 8. This shaft is provided with a series of rabble arms as at 9 and shaft into the space between succeeding hearths. Suitable rabble teeth 11. are pro,- vided on the rabble arms for advancing the material being treated successively over each of the hearths. A hopper is indicated at 12 for discharging the material to be treated into .the furnace through an ore-luted feeding device 13. As shown in the drawing, the top of the furnace may be surmounted by a support 14 and cross member 15. The material entering the furnace through the feeding" device 13 falls 'upon a delivery bed 16 where it is given a preliminary heating and is efi'ectivel dried. T 9 ar 3w maria tatable and internally cooled shaft extends through the furnace substan- 10 extending radially from the feed shelf 17 supported from the cross member 15 and upon whichthe material from the hopper falls and rests in a conical pile with a predetermined angle ofv repose depending upon the character of the material. T hed'imensions of this pile of ma terial maybe regulated by elevating or lowering an adjustable spout 18 which depends from the hopper l2 and the position of which is controlled by an adjustable supporting bolt and nut as indicated at 19. A rake or delivery arm 20 is secured to the rotating shaft 8 and is designed toengage the pile of ore or other material on the shelf 17, thereby delivering to the bed 16 once during each revolution of the shaft, as is well understood in the art, a predetermined quantity of material, depending upon the elevational adjustment of the spout 18 and upon the length of the arm 20 which may also be adjustable. The material which falls upon the delivery bed 16 is gradually advanced to a hopper 21 extending down from the delivery bed, such advancement of the material belng effected by one of the rabble arms 9 provided with teeth 11, which are positioned at an angle to deflect the material outwardly from the-center of the delivery bed toward the hopper 21. The hopper .21 forms a part of another" ore-luted feeding device, comprising a shelf 22 and delivery arm or rake 23, which cooperate with the hopper in a manner similar to the operation of the feeding device 13, as above described.

The material being treated falls from the shelf 22 and passes down through the furnace over the successive superposed hearths in the usual manner, alternate hearths being provided respectively with central and peripheral discharge openings so that the ore or other material isgradually advanced inwardly of one hearth toward the centralopening and outwardly over the next hearth toward the peripheral openings. For example, in the furnace-shown in the drawing, heart-h No. 1 is provided with an annular space 24 aronud the central shaft, which space comprises the central opening. The rabbleteeth over this hearth are directed at an angle for advancing-the material to w'ard such from the point where it falls from the shelf 22 near the peri hery of the hearth. Hearth No. 2 is provi ed with one or more peripheral openings as at 25 and the rabble teeth which cooperate with this opening and away hearth are arranged at an angle for deflect- 'ing the mat zenia l outwardly of the hearth where itj smade to fall through the Openings 25.

. Iii the well-known form of furnace of this general type, while the material is passed downwardly through the furnace, oxidizing gas such as heated air is made to follow the same path, either in the same direction or in the opposite direction upwardly through the furnace. For certain purposes, this method of operating the furnace is subject to disadvantages. For example, if kieselguhr or other material which becomes dried and finely divided, is treated in the furnace, a great quantity of dust arising from the agitated material will be carried along .with the rapidly flowing stream of gas and exhausted from the furnace with the gas,-, thus resulting in a. considerable loss of the material under treatment. A substantial percentage of the'dust is caused to be placed in suspension'by the stream of gas by reason of the fact that the gases are driven through the -same hearth openings through which the roasted material passes. This is particularly noticeable at the lowermost hearths where the material has become very dry and finely divided.

Furthermore, where the material being treated is passed downwardly through the funace over the various hearths and the heated gases are passed in the same or opposite direction over" the same path, ,it is often found difiicult to properly control temperature conditions within the furnace. For example, in the upper part of the furnace, where the material to be treated has just been introduced, comparatively low temperatures will often prevail not only because of the cold material being introduced,

ating. furnaces heretofore known. Agam,

- where the gases ascend directly through the material as it drops through the various openings from hearth to hearth, combustion of the material may take place at such'material drops,-often toan undesirable extent,

resultingjn excessive temperatures and consequent formation of metallurgical combinations which are detrimental to the roasted product. With a view to eliminating or substantially minimizing a part or all of these diificulties which have been heretofore encountered, the novel arrangement of gas and material openings as here shown at hearths Nos. 3, 4 and 5 have been provided. Through hearth N o. 3which normally would be provided with a central opening, such as the opening 24 through hearth No. 1, an extra large opening -26 is here provided. The material falls from hearth No. 3 over the edge of the hearth but only around the periphery of the opening 26, leaving the space adjacent the shaft free for the upward flow of the stream of gas. Hearth No. 4 which would normally be provided only with peripheral discharge openings, is here shown as also provided with a central opening 27 for gas only, whereas peripheral openings 28 are provided for the material.- The major portion of the stream of gas is allowed to pass upwardly through the opening 27, and therefore the peripheral openings 28 through this hearth are-made somewhat smaller or fewer than the peripheral open+ ings 25 above referred to. Thus entirely independent openings are provided through this hearth respectively for the material being treated and for the rising oxidizing. gases. As above stated, the central opening 26 through hearth No. 3 is made large. This is done not only to provide ample space both for the stream of gasand the falling material but also to insurethe dropping of the material upon the hearth below without danger of the material falling through the central opening 27. Hearth No. 5 may be provided'with a central opening 29, the inner or central portions of which provide ample space for a gas path and the peripheral part of which opening provides a .material discharge space. relatively smaller than, the opening 26 inasmuch as hearth No. 6, the last hearth, has no central opening through which the material may fall.

In operating the furnace any suitable source of heat may be applied at any hearth consistent with metallurgical practice. For

.example, an oil torch or torches may be in troduced through suitable port openings as at The roasted material may discharged from the hearth No. 6 in the ordinary manner' through suitable openings therethrough(not shown)..

The heated gases rising from hearth N o. 6 are permitted to flow; in a direct path following the central shaft through the vario'us vertically aligned openings '29, 27 and 26 and although a portionof such gases and the heat'thereof may be imparted to the hearths 5 and 4, the major portion of such heated gas will be delivered to the upper hearths, thus insuring a satisfactory high working temperature at the upper part of .the furnace. On the other hand, in the lower part of the furnace, where the. matrial has already reached high temperatures, excessive heating is avoided. /Also, at the This opening may be fit) lower hearths where the gases are at the highest temperature, the stream of gas fol: lows a path more or less spaced from the falling ore at each opening, thus substantially reducing the undesirable combustion at such points. I

Although the invention is here shown as applied to a furnace having six hearths, the same principles may be embodied in furnaces of different dimensions and those having a larger or smaller number of hearths. For example. in a furnace having -12'hearths,'

it may be. desirable to provide central openings for by-passing the gas past 2 or more groups of 3 hearths, corresponding to hearths Nos. 3, 41- and 5 here shown. In other instances. it is desirable to provide all of the heaiths with central gas passages. Although the gases are passed upwardly through the. particular furnace here shown,

the invention is of course also applicable to furnaces in which the gases follow a downward path through the furnace. In order to readily control maybe dispensed with altogether, If smaller openings aredesired, the rings may be replaced by other rings having smaller'central openings. i

It will thus be seen that means are provided entirely within the furnace for bypassing the oxidizing gases, directly past a desired number of hearths, such means being adjustable if desired) Since the gases are by-passed through openings at the center of the furnace, no heat is Wasted by radiation as would be the case if gas passages were provided from hearth to hearth at theperiphery of the hearths or exteriorly of the furnace.

The usual practice as followed in the design of'furnaces of this general type may be followed as to constructional details whichare not specifically referred to herein.

lVhile the invention has been described in detail with respect to certain particularpre ferred examples which. give satisfactory results, it will be understood by those skilled therefore in the appended claims to cover all such changes and modifications.

temperatureconditions throughout the furnace to pro-.

lVhatis claimed as new and upon which it is desired to secure Letters Patent is:

1. In a furnace having a plurality of vertically spaced circular hearths surrounded by a cylindrical furnace wall, a rotatable shaft passing vertically through the center of the hearths, a series of rabble arms radiating from said shaft over the several hearths, alternate hearths being formed respectively with central and peripheral material discharge openings allowing the mate rial under treatment to drop from each hearth to succeeding hearths, and said rabble arms being provided with teeth for advancing the material over' each hearth toward the openings ofthat hearth, at least one of the hearths which has a peripheral opening bein r also formed with a central opening.

whieh together with the central openings in the hearths next below or above PIOVldGS a direct gas passage to the other hearths partially independent of the path ofthe 4 material being treated,

2.. In a furnace having a plurality of vertically spaced circular hearths surrounded hy a cylindrical furnace wall, a

rotatable shaft passing vertically through V the center of the hearths, a series of rabble several hearths, alternate hearths being formed respectively with central and peripheral material discharge openings allowing the material under treatment-to drop from each hearth to succeeding hearths, and

said rabble arms being provided with teeth for advancing the material over each hearth toward the openings of that he'artlnat least arms radiating from saidshaft over the imr three succeeding lowermost hearths being tically spaced circular hearths surrounded by a cylindrical furnace wall, a rotatable shaft passing vertically through the .center of the hearths, the next to the lowermost hearth having an opening around said shaft for admitting gas and discharging material, the second from the lowermost hearth having a material discharge opening at its pe ripher said s aft, and the third from the lowern'iost hearth having an opening around said shaft which is of substantially greater diameter than j the opening next below, whereby material is discharged to the next hearth below and gas ,is admitted directly from the lowermost hearth.

4t. In a furnace having a plurality of superposed hearthssurrounded by an insulating cylindrical furnace wall, a series of openings formed through successive hearths toprovide a path from-hearth to hearth for the material being treated, a

and a gas admitting opening at path for gasespassin through the furnace also being provided w olly within the inner limits of said furnace wall, at least a part of said path for gases comprising a by-pass leading directly past certain hearths and comprising hearth openings independent of said material openings.

5. In a furnace having a plurality of superposed hearths, a series of openings through the hearths to provide a path from hearth to hearth for the material being treated, the openings through successive hearths being offset from vertical align-.

ment, and a series of openings in vertical alignment through at least three of the hearths to 'provide'a direct path for gas passing through said three hearths. V

p 6. A closed furnace sealed against fugi-' tive escapement of gases and having a pluviding' a cessive hearth, passin rality of superposed hearths, openings hearths, which comprises passing the ore down through the furnace over each suca stream of heated oxidizing gas upwar 1y through the furnace, the temperature conditions in the furnace being controlled by allowingthe gas to follow a direct path past the lower hearthsdirectly to the upper hearths, and passing the gas along an upper hearth or the successive upperhearths, over the ore thereon.

8. The process of treatin'g dusty material hearth also being formed with openings sub stantially in alignment with said gas openon a plurality of superposed hearths in a furnace which'comprises passin the material' over each successive heart allowing the material to drop through openings in each hearth, to the succeeding hearth, and' passing a stream of hot past certain hearths, whereby eflicient roasting temperav tures are attained on all hearths.

10. A closed furnace sealed against fugi- I tive escapement of gases and havingv a pluraliy of superposedhearths, openings being formed through the hearths for passing material to be treated downwardl through the furnace, and rabbling means or advancing the material over each hearth towardthe" said openings'through such hearth, one of the intermediate hearths being formedwith a gas admitting opening substantially out of the path of the material, the hearths next above and below said intermediate hearth also being formed with openings substantially in alignment with said gas opening.

' 11. A furnace construction having a plurality of super osed hearths, openings being formed through the hearths for passing material to be treated downwardly through the furnace, and rabbling means for advancing the material over each hearth toward the said openings through such hearth, one of the intermediate hearths being formed with a gas admitting opening substantially out of the path of the material, the hearths next above and below 'saidintermediate ing.

In testimony whereof I have signed my name to this specification.

DUDLEY BAIRD. 

